This is considered the third book in Jones' Howl's Moving Castle world. It is also, by far, the worse. It still held the magical and whimsical quality of Howl's Moving Castle that I loved, but the main characters demolished the story.
Charmain Baker was asked by her uncle to house-sit while he's away. One day while staying at the house, a little boy named Peter appears on the doorstep and refuses to leave. In an attempt to get away from Peter (who causes massive chaos wherever he goes) Charmain accepts a job working in the king's library. However, her and Peter soon get wrapped-up in a mystery surrounding the disappearance of the the king's gold.
Charmain was an insufferable know-it-all. She's also relatively mean to Peter and comes across as quite spoiled. Peter was equally annoying. He was constantly ordering Charmain around and refused to listen to anyone. These traits would've been fine in both of the main characters, if they would have experienced any kind of character growth. But unfortunately, this never happens.
The only highlights of the novel were the parts with Sophie and Howl from Howl's Moving Castle. Both How and Sophie were still the same great characters from the first book. I loved getting a small glimpse into some of Sophie and Howl's adventures through these sequel books. However, I think I would've preferred to have read this story from their points-of-view. Charmain and Peter would've made much better side characters.
If you can get past the main characters' personalities the actual plot was very interesting. And the parts that featured more of the characters from the past two books and less of the two from this book were fantastic and really saved the story.